1. Field of the Invention
The present invention relates to a process for hydroprocessing a heavy hydrocarbon oil, in particular a process in which a mixture of two catalysts is used to obtain advantageous effects in the hydroprocessing of heavy hydrocarbon oils. The present invention also relates to a mixture of catalysts suitable for use in such a process.
2. Prior Art
Hydrocarbon oils containing 50 wt. % or more of components with a boiling point of 538° C. or higher are called heavy hydrocarbon oils. These include atmospheric residue (AR) and vacuum residue (VR), which are produced in petroleum refining. It is desired to remove impurities such as sulfur from these heavy hydrocarbon oils by hydroprocessing, and to convert them into lighter oils, which have a higher economic value.
The hydroprocessing of heavy hydrocarbon oils is done in ebullating bed operation or in fixed bed operation.
For ebullating bed operation, various catalysts have been proposed. Generally, these catalysts are capable of efficiently removing sulfur, Conradson carbon residue (CCR), various metals, nitrogen and/or asphaltenes. However, it was found that the decomposition of asphaltenes, an aggregate of condensed aromatic compounds which is in good balance with the rest of the feedstock, is generally accompanied by the formation of sediment and sludge.
Sediment can be determined by the Shell hot filtration solid test (SHFST). (see Van Kerkvoort et al., J. Inst. Pet., 37, pp. 596-604 (1951)). Its ordinary content is said to be about 0.19 to 1 wt. % in product with a boiling point of 340° C. or higher collected from the bottom of a flash drum.
Sediment formed during hydroprocessing may settle and deposit in such apparatuses as heat exchangers and reactors, and because it threatens to close off the passage, it can seriously hamper the operation of these apparatuses. Especially in the hydroprocessing of heavy hydrocarbon feeds containing large amounts of vacuum residue, sediment formation is an important factor, and there is therefore need for a process for effecting efficient contaminant removal in combination with low sediment formation and high conversion.
U.S. Pat. No. 5,100,855 describes a catalyst mixture for effecting hydrodemetallization, hydrodesulfurization, hydrodenitrogenation and hydroconversion of an asphaltene-containing feedstock, wherein one catalyst is a relatively small-pore catalyst and the other possesses a relatively large amount of macropore volume. The catalyst mixture is preferably applied in an ebullating bed. The first catalyst has less than 0.10 ml/g of pore volume in pores with a diameter above 200 Å, less than 0.02 ml/g in pores with a diameter above 800 Å, and a maximum average mesopore diameter of 130 Å. The second catalyst has more than 0.07 ml/g of pore volume in pores with a diameter of greater than 800 Å.
U.S. Pat. No. 6,086,749 describes a process and catalyst system for use in a moving bed, wherein a mixture of two types of catalysts is used, each designed for a different function such as hydrodemetallization and hydrodenitrogenation, respectively. At least one of the catalysts preferably has at least 75% of its pore volume in pores with a diameter of 100-300 Å, and less than 20% of its pore volume in pores with a diameter below 100 Å.
The object of the present invention is to provide an effective process for the hydroprocessing of a heavy hydrocarbon oil containing a large amount of impurities such as sulfur, Conradson carbon residue, metals, nitrogen, and asphaltene, for adequately removing the impurities. In addition to efficient contaminant removal, the process should show low sediment formation, high asphaltene removal, and high conversion. Further, it should possess high flexibility.
On the basis of diligent research, a catalytic hydroprocessing process was invented wherein a heavy oil is contacted with a mixture of two different hydrotreating catalysts, both catalysts meeting specific requirements as to surface area, pore volume, and pore size distribution. The first catalyst is specifically designed to decrease the impurities in the heavy hydrocarbon oil. In particular, it achieves efficient asphaltene removal in combination with hydrodemetallization. The second catalyst is tailored to effect advanced desulfurisation and hydrogenation reactions while inhibiting sediment formation due to asphaltene precipitation, to allow stable operation.
The use of a mixture of the two different catalysts leads to a synergistic effect resulting in a process showing stable operation, high contaminant removal and conversion activity, and low sediment formation, this in combination with great flexibility in operation.